[Devel] [PATCH vz10 v2] ve/proc/loadavg: sum nr_unint drift as signed long, not int

[Konstantin Khorenko]

cpu_cgroup_proc_loadavg() sums the per-CPU cfs_rq::nr_unint counters
into a plain int accumulator and prints it with %d:

	int nr_running = 0;
	...
	nr_running += tg->cfs_rq[i]->nr_unint;

nr_unint is unsigned long and relies on signed reinterpretation to
fold the migration drift: a task can increment it on one CPU while
the matching decrement lands on another CPU after migration, so a
single per-CPU value can be far negative (stored as a huge unsigned
number) and only the sum over all CPUs is meaningful.

This is not a wrong-value fix: reading the drift as signed and adding
it folds to the same small non-negative sum whether the accumulator
is int or long. The change is for consistency and clarity, not
correctness:

 - calc_load_fold_active() and calc_load_ve() fold the very same
   per-CPU nr_unint in a long with an explicit (long) cast; this site
   is the odd one out;
 - an explicit (long) cast states the signed reinterpretation at the
   read site instead of hiding it in an implicit unsigned-long-to-int
   narrowing;
 - a long accumulator prints correctly with %ld and could host a
   "< 0" sanity check like calc_load_ve() has.

Accumulate in long, cast each term with (long), print with %ld.

Fixes: e4a432fe473c ("ve/proc/loadavg: Virtualize /proc/loadavg in Containers")

Reported-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
https://virtuozzo.atlassian.net/browse/VSTOR-132310
Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 kernel/sched/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d51d70ff7560..d5b4d8c97a0c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10045,7 +10045,7 @@ int cpu_cgroup_proc_loadavg(struct cgroup_subsys_state *css,
 	struct cgroup *cgrp = css->cgroup;
 	struct task_group *tg = css_tg(css);
 	unsigned long avnrun[3];
-	int nr_running = 0;
+	long nr_running = 0;
 	int i;
 
 	if (!test_bit(CGRP_VE_ROOT, &cgrp->flags))
@@ -10064,14 +10064,14 @@ int cpu_cgroup_proc_loadavg(struct cgroup_subsys_state *css,
 		 * overhead for activate/deactivate operations. So, we
 		 * don't account child cgroup unint tasks here.
 		 */
-		nr_running += tg->cfs_rq[i]->nr_unint;
+		nr_running += (long)tg->cfs_rq[i]->nr_unint;
 #endif
 #ifdef CONFIG_RT_GROUP_SCHED
 		nr_running += tg->rt_rq[i]->rt_nr_running;
 #endif
 	}
 
-	seq_printf(p, "%lu.%02lu %lu.%02lu %lu.%02lu %d/%d %d\n",
+	seq_printf(p, "%lu.%02lu %lu.%02lu %lu.%02lu %ld/%d %d\n",
 		LOAD_INT(avnrun[0]), LOAD_FRAC(avnrun[0]),
 		LOAD_INT(avnrun[1]), LOAD_FRAC(avnrun[1]),
 		LOAD_INT(avnrun[2]), LOAD_FRAC(avnrun[2]),
-- 
2.47.1